sapi/was: skip shutdown unless FREE_AT_EXIT is set

The whole cleanup procedure is correct but is usually useless
overhead.  When you have ten thousand processes all shutting down at
the same time, that may take a while.  Let's skip this, but leave an
option to re-enable this by setting the environment variable
FREE_AT_EXIT=1 (similar to Ruby's "RUBY_FREE_AT_EXIT" environment
variable).

Author: MaxKellermann

sapi/was/was_main.c

@@ -711,6 +711,9 @@ RunWas(struct was_simple *w)
 			return false;
 	}
 
+	if (getenv("FREE_AT_EXIT") == NULL)
+		_exit(EXIT_SUCCESS);
+
 	return true;
 }
 
@@ -749,6 +752,9 @@ RunMultiWas(struct was_multi *m)
 		was_simple_free(w);
 	}
 
+	if (getenv("FREE_AT_EXIT") == NULL)
+		_exit(EXIT_SUCCESS);
+
 	sigaction(SIGCHLD, &old_sigchld, NULL);
 	return true;
 }